1 //=== StdLibraryFunctionsChecker.cpp - Model standard functions -*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This checker improves modeling of a few simple library functions. 10 // 11 // This checker provides a specification format - `Summary' - and 12 // contains descriptions of some library functions in this format. Each 13 // specification contains a list of branches for splitting the program state 14 // upon call, and range constraints on argument and return-value symbols that 15 // are satisfied on each branch. This spec can be expanded to include more 16 // items, like external effects of the function. 17 // 18 // The main difference between this approach and the body farms technique is 19 // in more explicit control over how many branches are produced. For example, 20 // consider standard C function `ispunct(int x)', which returns a non-zero value 21 // iff `x' is a punctuation character, that is, when `x' is in range 22 // ['!', '/'] [':', '@'] U ['[', '\`'] U ['{', '~']. 23 // `Summary' provides only two branches for this function. However, 24 // any attempt to describe this range with if-statements in the body farm 25 // would result in many more branches. Because each branch needs to be analyzed 26 // independently, this significantly reduces performance. Additionally, 27 // once we consider a branch on which `x' is in range, say, ['!', '/'], 28 // we assume that such branch is an important separate path through the program, 29 // which may lead to false positives because considering this particular path 30 // was not consciously intended, and therefore it might have been unreachable. 31 // 32 // This checker uses eval::Call for modeling pure functions (functions without 33 // side effets), for which their `Summary' is a precise model. This avoids 34 // unnecessary invalidation passes. Conflicts with other checkers are unlikely 35 // because if the function has no other effects, other checkers would probably 36 // never want to improve upon the modeling done by this checker. 37 // 38 // Non-pure functions, for which only partial improvement over the default 39 // behavior is expected, are modeled via check::PostCall, non-intrusively. 40 // 41 // The following standard C functions are currently supported: 42 // 43 // fgetc getline isdigit isupper 44 // fread isalnum isgraph isxdigit 45 // fwrite isalpha islower read 46 // getc isascii isprint write 47 // getchar isblank ispunct 48 // getdelim iscntrl isspace 49 // 50 //===----------------------------------------------------------------------===// 51 52 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 53 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 54 #include "clang/StaticAnalyzer/Core/Checker.h" 55 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 56 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" 57 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 58 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h" 59 60 using namespace clang; 61 using namespace clang::ento; 62 63 namespace { 64 class StdLibraryFunctionsChecker 65 : public Checker<check::PreCall, check::PostCall, eval::Call> { 66 /// Below is a series of typedefs necessary to define function specs. 67 /// We avoid nesting types here because each additional qualifier 68 /// would need to be repeated in every function spec. 69 struct Summary; 70 71 /// Specify how much the analyzer engine should entrust modeling this function 72 /// to us. If he doesn't, he performs additional invalidations. 73 enum InvalidationKind { NoEvalCall, EvalCallAsPure }; 74 75 // The universal integral type to use in value range descriptions. 76 // Unsigned to make sure overflows are well-defined. 77 typedef uint64_t RangeInt; 78 79 /// Normally, describes a single range constraint, eg. {{0, 1}, {3, 4}} is 80 /// a non-negative integer, which less than 5 and not equal to 2. For 81 /// `ComparesToArgument', holds information about how exactly to compare to 82 /// the argument. 83 typedef std::vector<std::pair<RangeInt, RangeInt>> IntRangeVector; 84 85 /// A reference to an argument or return value by its number. 86 /// ArgNo in CallExpr and CallEvent is defined as Unsigned, but 87 /// obviously uint32_t should be enough for all practical purposes. 88 typedef uint32_t ArgNo; 89 static const ArgNo Ret; 90 91 class ValueConstraint; 92 93 // Pointer to the ValueConstraint. We need a copyable, polymorphic and 94 // default initialize able type (vector needs that). A raw pointer was good, 95 // however, we cannot default initialize that. unique_ptr makes the Summary 96 // class non-copyable, therefore not an option. Releasing the copyability 97 // requirement would render the initialization of the Summary map infeasible. 98 using ValueConstraintPtr = std::shared_ptr<ValueConstraint>; 99 100 /// Polymorphic base class that represents a constraint on a given argument 101 /// (or return value) of a function. Derived classes implement different kind 102 /// of constraints, e.g range constraints or correlation between two 103 /// arguments. 104 class ValueConstraint { 105 public: 106 ValueConstraint(ArgNo ArgN) : ArgN(ArgN) {} 107 virtual ~ValueConstraint() {} 108 /// Apply the effects of the constraint on the given program state. If null 109 /// is returned then the constraint is not feasible. 110 virtual ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 111 const Summary &Summary) const = 0; 112 virtual ValueConstraintPtr negate() const { 113 llvm_unreachable("Not implemented"); 114 }; 115 ArgNo getArgNo() const { return ArgN; } 116 117 protected: 118 ArgNo ArgN; // Argument to which we apply the constraint. 119 }; 120 121 /// Given a range, should the argument stay inside or outside this range? 122 enum RangeKind { OutOfRange, WithinRange }; 123 124 /// Encapsulates a single range on a single symbol within a branch. 125 class RangeConstraint : public ValueConstraint { 126 RangeKind Kind; // Kind of range definition. 127 IntRangeVector Args; // Polymorphic arguments. 128 129 public: 130 RangeConstraint(ArgNo ArgN, RangeKind Kind, const IntRangeVector &Args) 131 : ValueConstraint(ArgN), Kind(Kind), Args(Args) {} 132 133 const IntRangeVector &getRanges() const { 134 return Args; 135 } 136 137 private: 138 ProgramStateRef applyAsOutOfRange(ProgramStateRef State, 139 const CallEvent &Call, 140 const Summary &Summary) const; 141 ProgramStateRef applyAsWithinRange(ProgramStateRef State, 142 const CallEvent &Call, 143 const Summary &Summary) const; 144 public: 145 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 146 const Summary &Summary) const override { 147 switch (Kind) { 148 case OutOfRange: 149 return applyAsOutOfRange(State, Call, Summary); 150 case WithinRange: 151 return applyAsWithinRange(State, Call, Summary); 152 } 153 llvm_unreachable("Unknown range kind!"); 154 } 155 156 ValueConstraintPtr negate() const override { 157 RangeConstraint Tmp(*this); 158 switch (Kind) { 159 case OutOfRange: 160 Tmp.Kind = WithinRange; 161 break; 162 case WithinRange: 163 Tmp.Kind = OutOfRange; 164 break; 165 } 166 return std::make_shared<RangeConstraint>(Tmp); 167 } 168 }; 169 170 class ComparisonConstraint : public ValueConstraint { 171 BinaryOperator::Opcode Opcode; 172 ArgNo OtherArgN; 173 174 public: 175 ComparisonConstraint(ArgNo ArgN, BinaryOperator::Opcode Opcode, 176 ArgNo OtherArgN) 177 : ValueConstraint(ArgN), Opcode(Opcode), OtherArgN(OtherArgN) {} 178 ArgNo getOtherArgNo() const { return OtherArgN; } 179 BinaryOperator::Opcode getOpcode() const { return Opcode; } 180 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 181 const Summary &Summary) const override; 182 }; 183 184 class NotNullConstraint : public ValueConstraint { 185 using ValueConstraint::ValueConstraint; 186 // This variable has a role when we negate the constraint. 187 bool CannotBeNull = true; 188 189 public: 190 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 191 const Summary &Summary) const override { 192 SVal V = getArgSVal(Call, getArgNo()); 193 if (V.isUndef()) 194 return State; 195 196 DefinedOrUnknownSVal L = V.castAs<DefinedOrUnknownSVal>(); 197 if (!L.getAs<Loc>()) 198 return State; 199 200 return State->assume(L, CannotBeNull); 201 } 202 203 ValueConstraintPtr negate() const override { 204 NotNullConstraint Tmp(*this); 205 Tmp.CannotBeNull = !this->CannotBeNull; 206 return std::make_shared<NotNullConstraint>(Tmp); 207 } 208 }; 209 210 /// The complete list of constraints that defines a single branch. 211 typedef std::vector<ValueConstraintPtr> ConstraintSet; 212 213 using ArgTypes = std::vector<QualType>; 214 using Cases = std::vector<ConstraintSet>; 215 216 /// Includes information about 217 /// * function prototype (which is necessary to 218 /// ensure we're modeling the right function and casting values properly), 219 /// * approach to invalidation, 220 /// * a list of branches - a list of list of ranges - 221 /// A branch represents a path in the exploded graph of a function (which 222 /// is a tree). So, a branch is a series of assumptions. In other words, 223 /// branches represent split states and additional assumptions on top of 224 /// the splitting assumption. 225 /// For example, consider the branches in `isalpha(x)` 226 /// Branch 1) 227 /// x is in range ['A', 'Z'] or in ['a', 'z'] 228 /// then the return value is not 0. (I.e. out-of-range [0, 0]) 229 /// Branch 2) 230 /// x is out-of-range ['A', 'Z'] and out-of-range ['a', 'z'] 231 /// then the return value is 0. 232 /// * a list of argument constraints, that must be true on every branch. 233 /// If these constraints are not satisfied that means a fatal error 234 /// usually resulting in undefined behaviour. 235 struct Summary { 236 const ArgTypes ArgTys; 237 const QualType RetTy; 238 const InvalidationKind InvalidationKd; 239 Cases CaseConstraints; 240 ConstraintSet ArgConstraints; 241 242 Summary(ArgTypes ArgTys, QualType RetTy, InvalidationKind InvalidationKd) 243 : ArgTys(ArgTys), RetTy(RetTy), InvalidationKd(InvalidationKd) {} 244 245 Summary &Case(ConstraintSet&& CS) { 246 CaseConstraints.push_back(std::move(CS)); 247 return *this; 248 } 249 Summary &ArgConstraint(ValueConstraintPtr VC) { 250 ArgConstraints.push_back(VC); 251 return *this; 252 } 253 254 private: 255 static void assertTypeSuitableForSummary(QualType T) { 256 assert(!T->isVoidType() && 257 "We should have had no significant void types in the spec"); 258 assert(T.isCanonical() && 259 "We should only have canonical types in the spec"); 260 } 261 262 public: 263 QualType getArgType(ArgNo ArgN) const { 264 QualType T = (ArgN == Ret) ? RetTy : ArgTys[ArgN]; 265 assertTypeSuitableForSummary(T); 266 return T; 267 } 268 269 /// Try our best to figure out if the call expression is the call of 270 /// *the* library function to which this specification applies. 271 bool matchesCall(const CallExpr *CE) const; 272 }; 273 274 // The same function (as in, function identifier) may have different 275 // summaries assigned to it, with different argument and return value types. 276 // We call these "variants" of the function. This can be useful for handling 277 // C++ function overloads, and also it can be used when the same function 278 // may have different definitions on different platforms. 279 typedef std::vector<Summary> Summaries; 280 281 // The map of all functions supported by the checker. It is initialized 282 // lazily, and it doesn't change after initialization. 283 mutable llvm::StringMap<Summaries> FunctionSummaryMap; 284 285 mutable std::unique_ptr<BugType> BT_InvalidArg; 286 287 // Auxiliary functions to support ArgNo within all structures 288 // in a unified manner. 289 static QualType getArgType(const Summary &Summary, ArgNo ArgN) { 290 return Summary.getArgType(ArgN); 291 } 292 static QualType getArgType(const CallEvent &Call, ArgNo ArgN) { 293 return ArgN == Ret ? Call.getResultType().getCanonicalType() 294 : Call.getArgExpr(ArgN)->getType().getCanonicalType(); 295 } 296 static QualType getArgType(const CallExpr *CE, ArgNo ArgN) { 297 return ArgN == Ret ? CE->getType().getCanonicalType() 298 : CE->getArg(ArgN)->getType().getCanonicalType(); 299 } 300 static SVal getArgSVal(const CallEvent &Call, ArgNo ArgN) { 301 return ArgN == Ret ? Call.getReturnValue() : Call.getArgSVal(ArgN); 302 } 303 304 public: 305 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 306 void checkPostCall(const CallEvent &Call, CheckerContext &C) const; 307 bool evalCall(const CallEvent &Call, CheckerContext &C) const; 308 309 enum CheckKind { 310 CK_StdCLibraryFunctionArgsChecker, 311 CK_StdCLibraryFunctionsTesterChecker, 312 CK_NumCheckKinds 313 }; 314 DefaultBool ChecksEnabled[CK_NumCheckKinds]; 315 CheckerNameRef CheckNames[CK_NumCheckKinds]; 316 317 private: 318 Optional<Summary> findFunctionSummary(const FunctionDecl *FD, 319 const CallExpr *CE, 320 CheckerContext &C) const; 321 Optional<Summary> findFunctionSummary(const CallEvent &Call, 322 CheckerContext &C) const; 323 324 void initFunctionSummaries(CheckerContext &C) const; 325 326 void reportBug(const CallEvent &Call, ExplodedNode *N, 327 CheckerContext &C) const { 328 if (!ChecksEnabled[CK_StdCLibraryFunctionArgsChecker]) 329 return; 330 // TODO Add detailed diagnostic. 331 StringRef Msg = "Function argument constraint is not satisfied"; 332 if (!BT_InvalidArg) 333 BT_InvalidArg = std::make_unique<BugType>( 334 CheckNames[CK_StdCLibraryFunctionArgsChecker], 335 "Unsatisfied argument constraints", categories::LogicError); 336 auto R = std::make_unique<PathSensitiveBugReport>(*BT_InvalidArg, Msg, N); 337 bugreporter::trackExpressionValue(N, Call.getArgExpr(0), *R); 338 C.emitReport(std::move(R)); 339 } 340 }; 341 342 const StdLibraryFunctionsChecker::ArgNo StdLibraryFunctionsChecker::Ret = 343 std::numeric_limits<ArgNo>::max(); 344 345 } // end of anonymous namespace 346 347 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsOutOfRange( 348 ProgramStateRef State, const CallEvent &Call, 349 const Summary &Summary) const { 350 351 ProgramStateManager &Mgr = State->getStateManager(); 352 SValBuilder &SVB = Mgr.getSValBuilder(); 353 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 354 ConstraintManager &CM = Mgr.getConstraintManager(); 355 QualType T = getArgType(Summary, getArgNo()); 356 SVal V = getArgSVal(Call, getArgNo()); 357 358 if (auto N = V.getAs<NonLoc>()) { 359 const IntRangeVector &R = getRanges(); 360 size_t E = R.size(); 361 for (size_t I = 0; I != E; ++I) { 362 const llvm::APSInt &Min = BVF.getValue(R[I].first, T); 363 const llvm::APSInt &Max = BVF.getValue(R[I].second, T); 364 assert(Min <= Max); 365 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 366 if (!State) 367 break; 368 } 369 } 370 371 return State; 372 } 373 374 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsWithinRange( 375 ProgramStateRef State, const CallEvent &Call, 376 const Summary &Summary) const { 377 378 ProgramStateManager &Mgr = State->getStateManager(); 379 SValBuilder &SVB = Mgr.getSValBuilder(); 380 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 381 ConstraintManager &CM = Mgr.getConstraintManager(); 382 QualType T = getArgType(Summary, getArgNo()); 383 SVal V = getArgSVal(Call, getArgNo()); 384 385 // "WithinRange R" is treated as "outside [T_MIN, T_MAX] \ R". 386 // We cut off [T_MIN, min(R) - 1] and [max(R) + 1, T_MAX] if necessary, 387 // and then cut away all holes in R one by one. 388 // 389 // E.g. consider a range list R as [A, B] and [C, D] 390 // -------+--------+------------------+------------+-----------> 391 // A B C D 392 // Then we assume that the value is not in [-inf, A - 1], 393 // then not in [D + 1, +inf], then not in [B + 1, C - 1] 394 if (auto N = V.getAs<NonLoc>()) { 395 const IntRangeVector &R = getRanges(); 396 size_t E = R.size(); 397 398 const llvm::APSInt &MinusInf = BVF.getMinValue(T); 399 const llvm::APSInt &PlusInf = BVF.getMaxValue(T); 400 401 const llvm::APSInt &Left = BVF.getValue(R[0].first - 1ULL, T); 402 if (Left != PlusInf) { 403 assert(MinusInf <= Left); 404 State = CM.assumeInclusiveRange(State, *N, MinusInf, Left, false); 405 if (!State) 406 return nullptr; 407 } 408 409 const llvm::APSInt &Right = BVF.getValue(R[E - 1].second + 1ULL, T); 410 if (Right != MinusInf) { 411 assert(Right <= PlusInf); 412 State = CM.assumeInclusiveRange(State, *N, Right, PlusInf, false); 413 if (!State) 414 return nullptr; 415 } 416 417 for (size_t I = 1; I != E; ++I) { 418 const llvm::APSInt &Min = BVF.getValue(R[I - 1].second + 1ULL, T); 419 const llvm::APSInt &Max = BVF.getValue(R[I].first - 1ULL, T); 420 if (Min <= Max) { 421 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 422 if (!State) 423 return nullptr; 424 } 425 } 426 } 427 428 return State; 429 } 430 431 ProgramStateRef StdLibraryFunctionsChecker::ComparisonConstraint::apply( 432 ProgramStateRef State, const CallEvent &Call, 433 const Summary &Summary) const { 434 435 ProgramStateManager &Mgr = State->getStateManager(); 436 SValBuilder &SVB = Mgr.getSValBuilder(); 437 QualType CondT = SVB.getConditionType(); 438 QualType T = getArgType(Summary, getArgNo()); 439 SVal V = getArgSVal(Call, getArgNo()); 440 441 BinaryOperator::Opcode Op = getOpcode(); 442 ArgNo OtherArg = getOtherArgNo(); 443 SVal OtherV = getArgSVal(Call, OtherArg); 444 QualType OtherT = getArgType(Call, OtherArg); 445 // Note: we avoid integral promotion for comparison. 446 OtherV = SVB.evalCast(OtherV, T, OtherT); 447 if (auto CompV = SVB.evalBinOp(State, Op, V, OtherV, CondT) 448 .getAs<DefinedOrUnknownSVal>()) 449 State = State->assume(*CompV, true); 450 return State; 451 } 452 453 void StdLibraryFunctionsChecker::checkPreCall(const CallEvent &Call, 454 CheckerContext &C) const { 455 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 456 if (!FoundSummary) 457 return; 458 459 const Summary &Summary = *FoundSummary; 460 ProgramStateRef State = C.getState(); 461 462 ProgramStateRef NewState = State; 463 for (const ValueConstraintPtr& VC : Summary.ArgConstraints) { 464 ProgramStateRef SuccessSt = VC->apply(NewState, Call, Summary); 465 ProgramStateRef FailureSt = VC->negate()->apply(NewState, Call, Summary); 466 // The argument constraint is not satisfied. 467 if (FailureSt && !SuccessSt) { 468 if (ExplodedNode *N = C.generateErrorNode(NewState)) 469 reportBug(Call, N, C); 470 break; 471 } else { 472 // We will apply the constraint even if we cannot reason about the 473 // argument. This means both SuccessSt and FailureSt can be true. If we 474 // weren't applying the constraint that would mean that symbolic 475 // execution continues on a code whose behaviour is undefined. 476 assert(SuccessSt); 477 NewState = SuccessSt; 478 } 479 } 480 if (NewState && NewState != State) 481 C.addTransition(NewState); 482 } 483 484 void StdLibraryFunctionsChecker::checkPostCall(const CallEvent &Call, 485 CheckerContext &C) const { 486 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 487 if (!FoundSummary) 488 return; 489 490 // Now apply the constraints. 491 const Summary &Summary = *FoundSummary; 492 ProgramStateRef State = C.getState(); 493 494 // Apply case/branch specifications. 495 for (const auto &VRS : Summary.CaseConstraints) { 496 ProgramStateRef NewState = State; 497 for (const auto &VR: VRS) { 498 NewState = VR->apply(NewState, Call, Summary); 499 if (!NewState) 500 break; 501 } 502 503 if (NewState && NewState != State) 504 C.addTransition(NewState); 505 } 506 } 507 508 bool StdLibraryFunctionsChecker::evalCall(const CallEvent &Call, 509 CheckerContext &C) const { 510 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 511 if (!FoundSummary) 512 return false; 513 514 const Summary &Summary = *FoundSummary; 515 switch (Summary.InvalidationKd) { 516 case EvalCallAsPure: { 517 ProgramStateRef State = C.getState(); 518 const LocationContext *LC = C.getLocationContext(); 519 const auto *CE = cast_or_null<CallExpr>(Call.getOriginExpr()); 520 SVal V = C.getSValBuilder().conjureSymbolVal( 521 CE, LC, CE->getType().getCanonicalType(), C.blockCount()); 522 State = State->BindExpr(CE, LC, V); 523 C.addTransition(State); 524 return true; 525 } 526 case NoEvalCall: 527 // Summary tells us to avoid performing eval::Call. The function is possibly 528 // evaluated by another checker, or evaluated conservatively. 529 return false; 530 } 531 llvm_unreachable("Unknown invalidation kind!"); 532 } 533 534 bool StdLibraryFunctionsChecker::Summary::matchesCall( 535 const CallExpr *CE) const { 536 // Check number of arguments: 537 if (CE->getNumArgs() != ArgTys.size()) 538 return false; 539 540 // Check return type if relevant: 541 if (!RetTy.isNull() && RetTy != CE->getType().getCanonicalType()) 542 return false; 543 544 // Check argument types when relevant: 545 for (size_t I = 0, E = ArgTys.size(); I != E; ++I) { 546 QualType FormalT = ArgTys[I]; 547 // Null type marks irrelevant arguments. 548 if (FormalT.isNull()) 549 continue; 550 551 assertTypeSuitableForSummary(FormalT); 552 553 QualType ActualT = StdLibraryFunctionsChecker::getArgType(CE, I); 554 assert(ActualT.isCanonical()); 555 if (ActualT != FormalT) 556 return false; 557 } 558 559 return true; 560 } 561 562 Optional<StdLibraryFunctionsChecker::Summary> 563 StdLibraryFunctionsChecker::findFunctionSummary(const FunctionDecl *FD, 564 const CallExpr *CE, 565 CheckerContext &C) const { 566 // Note: we cannot always obtain FD from CE 567 // (eg. virtual call, or call by pointer). 568 assert(CE); 569 570 if (!FD) 571 return None; 572 573 initFunctionSummaries(C); 574 575 IdentifierInfo *II = FD->getIdentifier(); 576 if (!II) 577 return None; 578 StringRef Name = II->getName(); 579 if (Name.empty() || !C.isCLibraryFunction(FD, Name)) 580 return None; 581 582 auto FSMI = FunctionSummaryMap.find(Name); 583 if (FSMI == FunctionSummaryMap.end()) 584 return None; 585 586 // Verify that function signature matches the spec in advance. 587 // Otherwise we might be modeling the wrong function. 588 // Strict checking is important because we will be conducting 589 // very integral-type-sensitive operations on arguments and 590 // return values. 591 const Summaries &SpecVariants = FSMI->second; 592 for (const Summary &Spec : SpecVariants) 593 if (Spec.matchesCall(CE)) 594 return Spec; 595 596 return None; 597 } 598 599 Optional<StdLibraryFunctionsChecker::Summary> 600 StdLibraryFunctionsChecker::findFunctionSummary(const CallEvent &Call, 601 CheckerContext &C) const { 602 const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl()); 603 if (!FD) 604 return None; 605 const CallExpr *CE = dyn_cast_or_null<CallExpr>(Call.getOriginExpr()); 606 if (!CE) 607 return None; 608 return findFunctionSummary(FD, CE, C); 609 } 610 611 void StdLibraryFunctionsChecker::initFunctionSummaries( 612 CheckerContext &C) const { 613 if (!FunctionSummaryMap.empty()) 614 return; 615 616 SValBuilder &SVB = C.getSValBuilder(); 617 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 618 const ASTContext &ACtx = BVF.getContext(); 619 620 // These types are useful for writing specifications quickly, 621 // New specifications should probably introduce more types. 622 // Some types are hard to obtain from the AST, eg. "ssize_t". 623 // In such cases it should be possible to provide multiple variants 624 // of function summary for common cases (eg. ssize_t could be int or long 625 // or long long, so three summary variants would be enough). 626 // Of course, function variants are also useful for C++ overloads. 627 const QualType 628 Irrelevant{}; // A placeholder, whenever we do not care about the type. 629 const QualType IntTy = ACtx.IntTy; 630 const QualType LongTy = ACtx.LongTy; 631 const QualType LongLongTy = ACtx.LongLongTy; 632 const QualType SizeTy = ACtx.getSizeType(); 633 const QualType VoidPtrTy = ACtx.VoidPtrTy; // void *T 634 const QualType ConstVoidPtrTy = 635 ACtx.getPointerType(ACtx.VoidTy.withConst()); // const void *T 636 637 const RangeInt IntMax = BVF.getMaxValue(IntTy).getLimitedValue(); 638 const RangeInt LongMax = BVF.getMaxValue(LongTy).getLimitedValue(); 639 const RangeInt LongLongMax = BVF.getMaxValue(LongLongTy).getLimitedValue(); 640 641 // Set UCharRangeMax to min of int or uchar maximum value. 642 // The C standard states that the arguments of functions like isalpha must 643 // be representable as an unsigned char. Their type is 'int', so the max 644 // value of the argument should be min(UCharMax, IntMax). This just happen 645 // to be true for commonly used and well tested instruction set 646 // architectures, but not for others. 647 const RangeInt UCharRangeMax = 648 std::min(BVF.getMaxValue(ACtx.UnsignedCharTy).getLimitedValue(), IntMax); 649 650 // The platform dependent value of EOF. 651 // Try our best to parse this from the Preprocessor, otherwise fallback to -1. 652 const auto EOFv = [&C]() -> RangeInt { 653 if (const llvm::Optional<int> OptInt = 654 tryExpandAsInteger("EOF", C.getPreprocessor())) 655 return *OptInt; 656 return -1; 657 }(); 658 659 // We are finally ready to define specifications for all supported functions. 660 // 661 // The signature needs to have the correct number of arguments. 662 // However, we insert `Irrelevant' when the type is insignificant. 663 // 664 // Argument ranges should always cover all variants. If return value 665 // is completely unknown, omit it from the respective range set. 666 // 667 // All types in the spec need to be canonical. 668 // 669 // Every item in the list of range sets represents a particular 670 // execution path the analyzer would need to explore once 671 // the call is modeled - a new program state is constructed 672 // for every range set, and each range line in the range set 673 // corresponds to a specific constraint within this state. 674 // 675 // Upon comparing to another argument, the other argument is casted 676 // to the current argument's type. This avoids proper promotion but 677 // seems useful. For example, read() receives size_t argument, 678 // and its return value, which is of type ssize_t, cannot be greater 679 // than this argument. If we made a promotion, and the size argument 680 // is equal to, say, 10, then we'd impose a range of [0, 10] on the 681 // return value, however the correct range is [-1, 10]. 682 // 683 // Please update the list of functions in the header after editing! 684 // 685 686 // Below are helpers functions to create the summaries. 687 auto ArgumentCondition = [](ArgNo ArgN, RangeKind Kind, 688 IntRangeVector Ranges) { 689 return std::make_shared<RangeConstraint>(ArgN, Kind, Ranges); 690 }; 691 struct { 692 auto operator()(RangeKind Kind, IntRangeVector Ranges) { 693 return std::make_shared<RangeConstraint>(Ret, Kind, Ranges); 694 } 695 auto operator()(BinaryOperator::Opcode Op, ArgNo OtherArgN) { 696 return std::make_shared<ComparisonConstraint>(Ret, Op, OtherArgN); 697 } 698 } ReturnValueCondition; 699 auto Range = [](RangeInt b, RangeInt e) { 700 return IntRangeVector{std::pair<RangeInt, RangeInt>{b, e}}; 701 }; 702 auto SingleValue = [](RangeInt v) { 703 return IntRangeVector{std::pair<RangeInt, RangeInt>{v, v}}; 704 }; 705 auto LessThanOrEq = BO_LE; 706 auto NotNull = [&](ArgNo ArgN) { 707 return std::make_shared<NotNullConstraint>(ArgN); 708 }; 709 710 using RetType = QualType; 711 // Templates for summaries that are reused by many functions. 712 auto Getc = [&]() { 713 return Summary(ArgTypes{Irrelevant}, RetType{IntTy}, NoEvalCall) 714 .Case({ReturnValueCondition(WithinRange, 715 {{EOFv, EOFv}, {0, UCharRangeMax}})}); 716 }; 717 auto Read = [&](RetType R, RangeInt Max) { 718 return Summary(ArgTypes{Irrelevant, Irrelevant, SizeTy}, RetType{R}, 719 NoEvalCall) 720 .Case({ReturnValueCondition(LessThanOrEq, ArgNo(2)), 721 ReturnValueCondition(WithinRange, Range(-1, Max))}); 722 }; 723 auto Fread = [&]() { 724 return Summary(ArgTypes{VoidPtrTy, Irrelevant, SizeTy, Irrelevant}, 725 RetType{SizeTy}, NoEvalCall) 726 .Case({ 727 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 728 }) 729 .ArgConstraint(NotNull(ArgNo(0))); 730 }; 731 auto Fwrite = [&]() { 732 return Summary(ArgTypes{ConstVoidPtrTy, Irrelevant, SizeTy, Irrelevant}, 733 RetType{SizeTy}, NoEvalCall) 734 .Case({ 735 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 736 }) 737 .ArgConstraint(NotNull(ArgNo(0))); 738 }; 739 auto Getline = [&](RetType R, RangeInt Max) { 740 return Summary(ArgTypes{Irrelevant, Irrelevant, Irrelevant}, RetType{R}, 741 NoEvalCall) 742 .Case({ReturnValueCondition(WithinRange, {{-1, -1}, {1, Max}})}); 743 }; 744 745 FunctionSummaryMap = { 746 // The isascii() family of functions. 747 // The behavior is undefined if the value of the argument is not 748 // representable as unsigned char or is not equal to EOF. See e.g. C99 749 // 7.4.1.2 The isalpha function (p: 181-182). 750 { 751 "isalnum", 752 Summaries{ 753 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 754 // Boils down to isupper() or islower() or isdigit(). 755 .Case( 756 {ArgumentCondition(0U, WithinRange, 757 {{'0', '9'}, {'A', 'Z'}, {'a', 'z'}}), 758 ReturnValueCondition(OutOfRange, SingleValue(0))}) 759 // The locale-specific range. 760 // No post-condition. We are completely unaware of 761 // locale-specific return values. 762 .Case({ArgumentCondition(0U, WithinRange, 763 {{128, UCharRangeMax}})}) 764 .Case({ArgumentCondition(0U, OutOfRange, 765 {{'0', '9'}, 766 {'A', 'Z'}, 767 {'a', 'z'}, 768 {128, UCharRangeMax}}), 769 ReturnValueCondition(WithinRange, SingleValue(0))}) 770 .ArgConstraint(ArgumentCondition( 771 0U, WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}}))}, 772 }, 773 { 774 "isalpha", 775 Summaries{ 776 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 777 .Case({ArgumentCondition(0U, WithinRange, 778 {{'A', 'Z'}, {'a', 'z'}}), 779 ReturnValueCondition(OutOfRange, SingleValue(0))}) 780 // The locale-specific range. 781 .Case({ArgumentCondition(0U, WithinRange, 782 {{128, UCharRangeMax}})}) 783 .Case({ArgumentCondition( 784 0U, OutOfRange, 785 {{'A', 'Z'}, {'a', 'z'}, {128, UCharRangeMax}}), 786 ReturnValueCondition(WithinRange, SingleValue(0))})}, 787 }, 788 { 789 "isascii", 790 Summaries{ 791 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 792 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 793 ReturnValueCondition(OutOfRange, SingleValue(0))}) 794 .Case({ArgumentCondition(0U, OutOfRange, Range(0, 127)), 795 ReturnValueCondition(WithinRange, SingleValue(0))})}, 796 }, 797 { 798 "isblank", 799 Summaries{ 800 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 801 .Case({ArgumentCondition(0U, WithinRange, 802 {{'\t', '\t'}, {' ', ' '}}), 803 ReturnValueCondition(OutOfRange, SingleValue(0))}) 804 .Case({ArgumentCondition(0U, OutOfRange, 805 {{'\t', '\t'}, {' ', ' '}}), 806 ReturnValueCondition(WithinRange, SingleValue(0))})}, 807 }, 808 { 809 "iscntrl", 810 Summaries{ 811 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 812 .Case({ArgumentCondition(0U, WithinRange, 813 {{0, 32}, {127, 127}}), 814 ReturnValueCondition(OutOfRange, SingleValue(0))}) 815 .Case( 816 {ArgumentCondition(0U, OutOfRange, {{0, 32}, {127, 127}}), 817 ReturnValueCondition(WithinRange, SingleValue(0))})}, 818 }, 819 { 820 "isdigit", 821 Summaries{ 822 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 823 .Case({ArgumentCondition(0U, WithinRange, Range('0', '9')), 824 ReturnValueCondition(OutOfRange, SingleValue(0))}) 825 .Case({ArgumentCondition(0U, OutOfRange, Range('0', '9')), 826 ReturnValueCondition(WithinRange, SingleValue(0))})}, 827 }, 828 { 829 "isgraph", 830 Summaries{ 831 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 832 .Case({ArgumentCondition(0U, WithinRange, Range(33, 126)), 833 ReturnValueCondition(OutOfRange, SingleValue(0))}) 834 .Case({ArgumentCondition(0U, OutOfRange, Range(33, 126)), 835 ReturnValueCondition(WithinRange, SingleValue(0))})}, 836 }, 837 { 838 "islower", 839 Summaries{ 840 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 841 // Is certainly lowercase. 842 .Case({ArgumentCondition(0U, WithinRange, Range('a', 'z')), 843 ReturnValueCondition(OutOfRange, SingleValue(0))}) 844 // Is ascii but not lowercase. 845 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 846 ArgumentCondition(0U, OutOfRange, Range('a', 'z')), 847 ReturnValueCondition(WithinRange, SingleValue(0))}) 848 // The locale-specific range. 849 .Case({ArgumentCondition(0U, WithinRange, 850 {{128, UCharRangeMax}})}) 851 // Is not an unsigned char. 852 .Case({ArgumentCondition(0U, OutOfRange, 853 Range(0, UCharRangeMax)), 854 ReturnValueCondition(WithinRange, SingleValue(0))})}, 855 }, 856 { 857 "isprint", 858 Summaries{ 859 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 860 .Case({ArgumentCondition(0U, WithinRange, Range(32, 126)), 861 ReturnValueCondition(OutOfRange, SingleValue(0))}) 862 .Case({ArgumentCondition(0U, OutOfRange, Range(32, 126)), 863 ReturnValueCondition(WithinRange, SingleValue(0))})}, 864 }, 865 { 866 "ispunct", 867 Summaries{ 868 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 869 .Case({ArgumentCondition( 870 0U, WithinRange, 871 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 872 ReturnValueCondition(OutOfRange, SingleValue(0))}) 873 .Case({ArgumentCondition( 874 0U, OutOfRange, 875 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 876 ReturnValueCondition(WithinRange, SingleValue(0))})}, 877 }, 878 { 879 "isspace", 880 Summaries{ 881 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 882 // Space, '\f', '\n', '\r', '\t', '\v'. 883 .Case({ArgumentCondition(0U, WithinRange, 884 {{9, 13}, {' ', ' '}}), 885 ReturnValueCondition(OutOfRange, SingleValue(0))}) 886 // The locale-specific range. 887 .Case({ArgumentCondition(0U, WithinRange, 888 {{128, UCharRangeMax}})}) 889 .Case({ArgumentCondition( 890 0U, OutOfRange, 891 {{9, 13}, {' ', ' '}, {128, UCharRangeMax}}), 892 ReturnValueCondition(WithinRange, SingleValue(0))})}, 893 }, 894 { 895 "isupper", 896 Summaries{ 897 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 898 // Is certainly uppercase. 899 .Case({ArgumentCondition(0U, WithinRange, Range('A', 'Z')), 900 ReturnValueCondition(OutOfRange, SingleValue(0))}) 901 // The locale-specific range. 902 .Case({ArgumentCondition(0U, WithinRange, 903 {{128, UCharRangeMax}})}) 904 // Other. 905 .Case({ArgumentCondition(0U, OutOfRange, 906 {{'A', 'Z'}, {128, UCharRangeMax}}), 907 ReturnValueCondition(WithinRange, SingleValue(0))})}, 908 }, 909 { 910 "isxdigit", 911 Summaries{ 912 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 913 .Case( 914 {ArgumentCondition(0U, WithinRange, 915 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 916 ReturnValueCondition(OutOfRange, SingleValue(0))}) 917 .Case( 918 {ArgumentCondition(0U, OutOfRange, 919 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 920 ReturnValueCondition(WithinRange, SingleValue(0))})}, 921 }, 922 923 // The getc() family of functions that returns either a char or an EOF. 924 {"getc", Summaries{Getc()}}, 925 {"fgetc", Summaries{Getc()}}, 926 {"getchar", 927 Summaries{Summary(ArgTypes{}, RetType{IntTy}, NoEvalCall) 928 .Case({ReturnValueCondition( 929 WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}})})}}, 930 931 // read()-like functions that never return more than buffer size. 932 // We are not sure how ssize_t is defined on every platform, so we 933 // provide three variants that should cover common cases. 934 {"read", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax), 935 Read(LongLongTy, LongLongMax)}}, 936 {"write", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax), 937 Read(LongLongTy, LongLongMax)}}, 938 {"fread", Summaries{Fread()}}, 939 {"fwrite", Summaries{Fwrite()}}, 940 // getline()-like functions either fail or read at least the delimiter. 941 {"getline", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax), 942 Getline(LongLongTy, LongLongMax)}}, 943 {"getdelim", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax), 944 Getline(LongLongTy, LongLongMax)}}, 945 }; 946 947 // Functions for testing. 948 if (ChecksEnabled[CK_StdCLibraryFunctionsTesterChecker]) { 949 llvm::StringMap<Summaries> TestFunctionSummaryMap = { 950 {"__two_constrained_args", 951 Summaries{ 952 Summary(ArgTypes{IntTy, IntTy}, RetType{IntTy}, EvalCallAsPure) 953 .ArgConstraint( 954 ArgumentCondition(0U, WithinRange, SingleValue(1))) 955 .ArgConstraint( 956 ArgumentCondition(1U, WithinRange, SingleValue(1)))}}, 957 {"__arg_constrained_twice", 958 Summaries{Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 959 .ArgConstraint( 960 ArgumentCondition(0U, OutOfRange, SingleValue(1))) 961 .ArgConstraint( 962 ArgumentCondition(0U, OutOfRange, SingleValue(2)))}}, 963 {"__defaultparam", Summaries{Summary(ArgTypes{Irrelevant, IntTy}, 964 RetType{IntTy}, EvalCallAsPure) 965 .ArgConstraint(NotNull(ArgNo(0)))}}, 966 }; 967 for (auto &E : TestFunctionSummaryMap) { 968 auto InsertRes = 969 FunctionSummaryMap.insert({std::string(E.getKey()), E.getValue()}); 970 assert(InsertRes.second && 971 "Test functions must not clash with modeled functions"); 972 (void)InsertRes; 973 } 974 } 975 } 976 977 void ento::registerStdCLibraryFunctionsChecker(CheckerManager &mgr) { 978 mgr.registerChecker<StdLibraryFunctionsChecker>(); 979 } 980 981 bool ento::shouldRegisterStdCLibraryFunctionsChecker(const CheckerManager &mgr) { 982 return true; 983 } 984 985 #define REGISTER_CHECKER(name) \ 986 void ento::register##name(CheckerManager &mgr) { \ 987 StdLibraryFunctionsChecker *checker = \ 988 mgr.getChecker<StdLibraryFunctionsChecker>(); \ 989 checker->ChecksEnabled[StdLibraryFunctionsChecker::CK_##name] = true; \ 990 checker->CheckNames[StdLibraryFunctionsChecker::CK_##name] = \ 991 mgr.getCurrentCheckerName(); \ 992 } \ 993 \ 994 bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; } 995 996 REGISTER_CHECKER(StdCLibraryFunctionArgsChecker) 997 REGISTER_CHECKER(StdCLibraryFunctionsTesterChecker) 998